Laszlo Ersek
2021-Dec-08 12:20 UTC
[Libguestfs] [virt-v2v PATCH 1/3] lib/nbdkit: add the "Nbdkit.with_connect_unix" helper function
Connecting to an NBD server temporarily, for a "one-shot" operation,
is
quite similar to "Std_utils.with_open_in" and
"Std_utils.with_open_out",
as there are cleanup operations regardless of whether the "one-shot"
operation completes successfully or throws an exception.
Introduce the "Nbdkit.with_connect_unix" function, which takes a Unix
domain socket pathname, a list of metadata contexts to request from the
NBD server, and calls a function with the live NBD server connection.
Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2027598
Signed-off-by: Laszlo Ersek <lersek at redhat.com>
---
lib/Makefile.am | 2 +-
lib/nbdkit.mli | 10 ++++++++++
lib/nbdkit.ml | 12 ++++++++++++
3 files changed, 23 insertions(+), 1 deletion(-)
diff --git a/lib/Makefile.am b/lib/Makefile.am
index c274b9ecf6c7..1fab25b326f5 100644
--- a/lib/Makefile.am
+++ b/lib/Makefile.am
@@ -80,7 +80,7 @@ BOBJECTS = config.cmo $(SOURCES_ML:.ml=.cmo)
XOBJECTS = $(BOBJECTS:.cmo=.cmx)
OCAMLPACKAGES = \
- -package str,unix \
+ -package str,unix,nbd \
-I $(builddir) \
-I $(top_builddir)/common/mlgettext \
-I $(top_builddir)/common/mlpcre \
diff --git a/lib/nbdkit.mli b/lib/nbdkit.mli
index ae19295186ed..825755e61dbe 100644
--- a/lib/nbdkit.mli
+++ b/lib/nbdkit.mli
@@ -107,3 +107,13 @@ val run_unix : ?socket:string -> cmd -> string * int
The --exit-with-parent, --foreground, --pidfile, --newstyle and
--unix flags are added automatically. Other flags are set as
in the {!cmd} struct. *)
+
+val with_connect_unix : socket:string ->
+ meta_contexts:string list ->
+ f:(NBD.t -> 'a) ->
+ 'a
+(** [with_connect_unix socket meta_contexts f] calls function [f] with the NBD
+ server at Unix domain socket [socket] connected, and the metadata contexts
+ in [meta_contexts] requested (each of which is not necessarily supported by
+ the server though). The connection is torn down either on normal return or
+ if the function [f] throws an exception. *)
diff --git a/lib/nbdkit.ml b/lib/nbdkit.ml
index 8d0bfdf9cff1..43e0fc5c728a 100644
--- a/lib/nbdkit.ml
+++ b/lib/nbdkit.ml
@@ -217,3 +217,15 @@ If the messages above are not sufficient to diagnose the
problem then add the
chmod socket 0o777;
socket, pid
+
+let with_connect_unix ~socket ~meta_contexts ~f + let nbd = NBD.create () in
+ protect
+ ~f:(fun () ->
+ List.iter (NBD.add_meta_context nbd) meta_contexts;
+ NBD.connect_unix nbd socket;
+ protect
+ ~f:(fun () -> f nbd)
+ ~finally:(fun () -> NBD.shutdown nbd)
+ )
+ ~finally:(fun () -> NBD.close nbd)
--
2.19.1.3.g30247aa5d201
Richard W.M. Jones
2021-Dec-08 15:18 UTC
[Libguestfs] [virt-v2v PATCH 1/3] lib/nbdkit: add the "Nbdkit.with_connect_unix" helper function
On Wed, Dec 08, 2021 at 01:20:48PM +0100, Laszlo Ersek wrote:> Connecting to an NBD server temporarily, for a "one-shot" operation, is > quite similar to "Std_utils.with_open_in" and "Std_utils.with_open_out", > as there are cleanup operations regardless of whether the "one-shot" > operation completes successfully or throws an exception. > > Introduce the "Nbdkit.with_connect_unix" function, which takes a Unix > domain socket pathname, a list of metadata contexts to request from the > NBD server, and calls a function with the live NBD server connection. > > Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2027598 > Signed-off-by: Laszlo Ersek <lersek at redhat.com> > --- > lib/Makefile.am | 2 +- > lib/nbdkit.mli | 10 ++++++++++ > lib/nbdkit.ml | 12 ++++++++++++ > 3 files changed, 23 insertions(+), 1 deletion(-) > > diff --git a/lib/Makefile.am b/lib/Makefile.am > index c274b9ecf6c7..1fab25b326f5 100644 > --- a/lib/Makefile.am > +++ b/lib/Makefile.am > @@ -80,7 +80,7 @@ BOBJECTS = config.cmo $(SOURCES_ML:.ml=.cmo) > XOBJECTS = $(BOBJECTS:.cmo=.cmx) > > OCAMLPACKAGES = \ > - -package str,unix \ > + -package str,unix,nbd \ > -I $(builddir) \ > -I $(top_builddir)/common/mlgettext \ > -I $(top_builddir)/common/mlpcre \ > diff --git a/lib/nbdkit.mli b/lib/nbdkit.mli > index ae19295186ed..825755e61dbe 100644 > --- a/lib/nbdkit.mli > +++ b/lib/nbdkit.mli > @@ -107,3 +107,13 @@ val run_unix : ?socket:string -> cmd -> string * int > The --exit-with-parent, --foreground, --pidfile, --newstyle and > --unix flags are added automatically. Other flags are set as > in the {!cmd} struct. *) > + > +val with_connect_unix : socket:string -> > + meta_contexts:string list -> > + f:(NBD.t -> 'a) -> > + 'a > +(** [with_connect_unix socket meta_contexts f] calls function [f] with the NBD > + server at Unix domain socket [socket] connected, and the metadata contexts > + in [meta_contexts] requested (each of which is not necessarily supported by > + the server though). The connection is torn down either on normal return or > + if the function [f] throws an exception. *)Interesting choice of module for this. nbdkit is a server. I would have put it into lib/utils.mli or created a new module. The function itself looks fine although personally I might have abstracted the meta_context function to be a "do anything between creation and connection" (let's call that "preparation"). What do you think about: val with_connect_unix : socket:string -> ?prepare:(NBD.t -> unit) -> f:(NBD.t -> 'a) -> 'a I think you would have to replace the List.iter line: ...> + ~f:(fun () ->(match prepare with Some pf -> pf nbd | None -> ());> + NBD.connect_unix nbd socket; > + protect > + ~f:(fun () -> f nbd) > + ~finally:(fun () -> NBD.shutdown nbd) > + ) > + ~finally:(fun () -> NBD.close nbd)It would be called like this: let prepare nbd = NBD.add_meta_context nbd "base:allocation" in with_connect_unix socket ~prepare ( fun () -> (* the code *) ) Hmm, maybe this is getting more complicated :-( Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com libguestfs lets you edit virtual machines. Supports shell scripting, bindings from many languages. http://libguestfs.org